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1.Thefirstphase-ordinaryselftappingscrew
Itisthedirectproductofearlysheetmetalscrews.Soitalsoknownasthe" sheetmetalscrew" .Itismainlyusedinthesheetmetalchanneltoconnectheatingandventilationsystem.Whenputitintothepreformedhole, makethemetalmaterialsshiftwhichareclosetotheholes, andatthesametimepushthemetalmaterialintothespacebetweenthescrewandthread.Asaresult, itformstheinternalthreadconnectingwithscrews.Thisistheearlist, themostbasicandthemostwidelyusedtappingscrew.
2.Thesecondphase-theselfcuttingtappingscrew
Becausetheordinaryselftappingscrewcanformthethreadonlyontherelativelythinandgoodtoughnesssheetmetalmaterial, itcannotbeappliedtothick, kemény, brittlematerialandmaterialwiththepoordeformationability.Thus, anewtypeofcommontappingscrews, Theselfcuttingtappingscrewwasborn.
3.Thethirdphase-theselfthreadingtappingscrew
Intheearly1950s, engineeringandtechnicalpersonneloffastenersdevelopedanewgenerationoftappingscrew - theselfthreadingtappingscrew.Thiskindofscrewhasthreadedrod (includingthread) androdend.
4.Thefourthphase-theselfdrillingtappingscrew
Theabovethreephasesofselftappingscrewhaveonethingincommoninuse: itisnecessarytoworkoutprefabricatedholeinadvancennthefittings.Thisisalsotheircommonweaknesses.So, intheearly1960s, engineersofspecialcustomscrewhavedevelopedtheselfdrillingtappingscrew.Thisisakindoftappingscrewwiththeshapeofdrillattheend.